In a conventional metal oxide semiconductor field effect transistor (MOSFET), the source, channel, and drain structures are constructed adjacent to each other within the same plane. Typically, a gate dielectric is formed on the channel area and a gate electrode is deposited on the gate dielectric. The transistor is controlled by applying a voltage to the gate electrode, thereby allowing a current to flow through the channel between source and drain.
An alternative to methods of building planar MOSFETs has been proposed to help alleviate some of the physical barriers to scaling down existing designs. The alternative method involves the construction of three dimensional MOSFETs, in the form of a multi-gate transistor such as a dual-gate field effect transistor (FinFET) or a tri-gate transistor field effect transistor, as a replacement for the conventional planar MOSFET.
Three-dimensional transistor designs such as the FinFET and the tri-gate field effect transistor allow tighter packing of the same number of transistors on a semiconductor chip by using vertical or angled surfaces for the gates. A tri-gate field effect transistor comprises three substantially equal length gates situated on three exposed surfaces of a diffused body whereas a FinFET comprises two equal length gates situated along the sides of a narrow diffused body, or fin.